Technical Abstract:
Whole-grain rice, especially the dark color bran rice, contains high phenolic content and antioxidant capacity, which have potential in disease prevention. However, little information is available regarding the differences in phytochemical profiles of rice of different bran color. Studies indicated that significant amounts of solvent-non-extractable, bound phytochemicals were present in other cereal grains. This study was aimed at determining unbound and bound phenolics and flavonoids contents, their iron chelating capability (ICC), total anthocyanin and tannin contents in 8 rice varieties with different bran color: 1 white, 2 light brown, 2 brown, 1 red, 2 purple. The content of these compounds in rice were compared with those of other cereal grains: corn, oat, red and white spring wheat, and barley. Flours were extracted with hexane, and then with AWA (acetone: water: acetic acid = 70: 29.5: 0.5) solvent for unbound phytochemicals. The residue was then treated with NaOH and extracted with ethyl acetate for bound phytochemicals. Total phenolic and flavonoid contents, including unbound and bound, in red and purple rice varieties (7.84-3.29 mg GAE (gallic acid equivalents)/g grain and 2.67-1.20 mg CE (catechin equivalents) per gram grain wt, respectively) were significantly greater than those in other rice varieties (1.39-1.04 mg GAE per gram grain wt and 0.53-0.44 mg CE per gram grain wt, respectively) (P less than 0.05) and other grains (5.23-2.04 mg GAE per gram grain wt and 1.92-0.57 mg CE per gram grain wt, respectively) (P less than 0.05). The portion of solvent extractable phenolics and flavonoids in red and purple rice (72.77-88.97 percent and 73.74-80.09 percent, respectively) were significantly higher than those in other rice varieties and other cereal grains (P less than 0.05). In addition, red and purple rice showed significantly higher total anthocyanin and tannin contents and ICC than other rice varieties and other grains (P less than 0.05). In conclusion, these results suggest that red and purple rice varieties show a great potential as the source of functional phytochemicals to provide beneficiary effects for human health.